Manufacturing method for small electric lamps

ABSTRACT

The present disclosure provides a new simplified method for manufacturing small electric lamps to be used within electronic equipment, particularly small electric lamps of long life and high quality, by heating from the outside of the bulb and fusing together the bulb and the bead of the bead mount attached with a filament, using equipment which can evacuate the inside and outside of the bulb separately; electric lamps thus produced; and the manufacturing equipment.

United States Patent [151 3,698,784 Hamai 1 Oct. 17, 1972 [54] MANUFACTURING METHOD FOR [56] References Cited SMALL ELECTRIC LAMPS UNITED STATES PATENTS [721 Invent: Japan 2,489,261 11/1949 Braunsdorff ..3l6/l9 [73] Assignee: Hamai Denkyu Kogyo Kabushiki 2,683,837 7/1954 Hager ..3l6/l9 i h Tokyo, Ja an 3,271,093 9/1966 Meier ..3l6/l9 Filed. April 14 1971 3,275,879 9/1966 Demarest et al ..3l6/l9 [211 App] 133 375 Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazarus Attorney-James E. Armstrong and Harold C. Wegner [30] Foreign Application Priority Data [57] ABSTRACT June 19,1970 Japan ,.45/539l4 June 19 1970 Japan ..45/53915 The Present dlschwe Promes new slmpllfied method for manufacturing small electric lamps to be used within electronic equipment, particularly small [52] US. Cl. ..3l6/19, 29/25.l5, 3311660128; electric ps of g life and g q y, y heating 51 l Cl from the outside of the bulb and fusing together the 1 23 bulb and the bead of the bead mount attached with a [58] held of can filament, using equipment which can evacuate the inside and outside of the bulb separately; electric lamps thus produced; and the manufacturing equipment.

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MANUFACTURING METHOD FOR SMALL ELECTRIC LAMPS BACKGROUND OF THE INVENTION In the manufacture of small electric lamps it is most important to ensure perfect fusion between the bead of the bead mount and the bulb and to prevent infiltration of impure gas into the bulb at the time of fusion.

The conventional manufacturing of small electric lamps has the following drawbacks. In one method the heating element, the bulb and the bead mountare all placed in an airtight box; after evacuating the airtight box, the-heating element is heated to fuse together the bulb and thebead of the bead mount. According to this method, when the heating element functions, impure gas generated from the bead and the heating element itself infiltrates into the bulb and gets sealed in the bulb, which is fused to the bead. As the result the degree of vacuum in the bulb drops and in consequence the small electric lamp thus produced cannot give-the required illumination, and its service life is shortened.

In another method, the bulb with its open end exposed and the bead mount with the bead exposed are held in a jig of high heat capacity and this jig is placed in a vacuum heating furnace. Then resistance wire around this furnace is heated to heat and fuse together the open end of the bulb and the bead of the bead mount. Next, heating is stopped and the jig is pulled out of the furnace by means of a metal wire attached to the jig. In this method, too, impure gas generated from the metal jig holding the bead mount and the bulb, the jig support and the metal-wire attached to this support, when they are heated, infiltrates into the bulb which is fused to the head of the beadv mount, and in consequence inevitably the same problems occur as in the first method. l

In still another method, the inside of the bulb, which holds the entire bead mount, is evacuated through the open end of the bulb by means of an exhaust pipe, etc.; then from outside of the bulb, the bulb and the bead of the bead mount are heated and fused together by'a gas burner, etc.

According to this method, the inside of the bulb is under vacuum and the outside of thebulb is under atmospheric pressure, with a wide difference in pressure between inside and outside of the bulb. Thus, when the burner is applied on the outside of the bulb, the bulb glass melts and softens, coming into contact withthe bead of the bead mount, before the bead of the bead mount can become soft enough to fuse with the bulb. This contactseems to result in fusion and sealing of the bead of the bead mount and the bulb, but actually the bead of the bead mount is often sealed while insufficiently softened. The lamps with thus imperfectly fused and sealed beads are liable to be cracked in service or develop a slow leak, leading to rejection out of service.

If the bead of the bead mount is melted and softened enough to fuse with the bulb, the above-mentioned troubles are not eliminated. Even then, when the bulb is heated externally, the bulb having a thinner wall, will be softened sooner than the bead of the bead mount; and with the inside of the bulb evacuated, the fused portion of the bulb will suffer greater deformation. This greater deformation will make the areas other than the fused portion between the bulb and the bead of the SUMMARY OF THE INVENTION The present invention. offers a new, simplified and cheap method, free from the drawbacks of the conventional methods, for manufacturing small electric lamps of high quality; small electric lamps thusproduced; and the manufacturing equipment. Using the present invention perfect fusion is assured of the bead of the bead mount to the bulb, which is free from deformed fusion, insufficient fusion or fusion strain, thereby making it possible to omit the annealing step for removal of fusion strain and to prevent rejects in productionfThe invention prevents infiltration intothe bulb of the impure gas generated from the heating element for heating the bead of the bead mount and the bulb and from the jig holding them. According to the present invention small electric lamps with no infiltration of impure gas in the bulb and perfect fusion of the head of the bead mount to the bulb are produced, thereby preventing development of cracks or slow leaks during service in lamps, preventing deterioration of, lamp illumination and prolonging the service life of the lamps. I

To fulfill these objectives, in this invention the inside and outside of the bulb are evacuated by providing an external cover with a clearance over the bulb which internally holds the filament-attached bead mount and separately creating a vacuum on the inside of the bulb and in the space between the bulb and the external cover; the bulb and the head of the bead mount are fused together by a heating ring installed around the part of the bulb to be fused, said ring being heated by high frequency means, or by a resistance heating element like a nichrome wire similarly installed around the bulb, said wire being supplied with electric current for heating; then with theunnecessary portion of the bulb cut off, small electric lamps are produced.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention, including small electric bulbs manufactured thereby and the manufacturing apparatus, will be clearly understood by reading the following detailed description with reference to the attached drawings.

Alterations or modifications in the details of this invention are covered by the appended claims.

In the attached drawings,

FIG. I shows an embodiment of the manufacturing apparatus for small electric lamps according to the present invention;

FIG. 2 shows another embodiment of the manufacturing apparatus according to the invention;

FIG. 3 and FIG. 4 are respectively partial perspective views of the embodiments in FIG. 1 and FIG. 2;

FIG. 5 is a cross sectional view illustrating the fusion between the bulb and the bead of the bead mount;

FIG. 6 is a sectional view of a finished product with the unnecessary portion of the bulb cutoff;

FIGS. 7, 8 and 10 are sectional views of apparatus for the conventional methods described above; and

FIG. 9 shows a partial enlargement of the apparatus of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION A detailed description of the manufacturing method of small electric lamps and the embodiments of apparatus according to the present invention is given in conjunction with the drawings; in each drawing the same symbol refers to the same component.

Referring to FIGS. 1, 3, 5 and 6, first, the upper side of a pair of lead wires 1, 2, separated by a certain gap, are beaded. Between the top ends of wires 11, 2, filament 3 is stretched, thereby constituting a bead mount a. Bead mount a, with the bottom of lead wires 1, 2 opened, is inserted into a soft glass bulb 4 with the top sealed and the bottom opened. Then, utilizing the elasticity of wires 1, 2, bead mount a is fixed in a predetermined position within bulb 4.

Next, at the outside of bulb 4 ring-holding cap 7b is fitted in such a position that high frequency heating carbon ring 6 may be positioned at the same level as head 5 of bead mount a.

With bead mount a thus inserted, the lower end of bulb 4, fitted withthe holding cap b for heating ring 6, is connected to charge-discharge communication hole 9 of evacuating circuit C linked to the evacuation equipment C equipped with vacuum cock 7 and air release cock 8; and in this state, evacuation or release of vacuum ismade.

Next, a hard glass external cover 11 with the top sealed and the bottom opened is provided, with a slight gap to the outside of bulb 4, over the entire bulb 4.

Gap 10 is arranged to communicate with another evacuating circuit C with a separate vacuum cock '12 and a separate air release cock 13 from said evacuation circuit C thus the inside of gap 10 can be evacuated or filled with air;

In this arrangement, nearly the entire external cover 11 is inserted into, for example, a known electric furnace of reversed V shape and the temperature in the space under external cover 11 and in the inside of bulb 4 is raised to heat and fuse together bulb 4 and bead 5 of the bead mount a. Thereby the small quantity of impure gas generated from the bulb 4 and the bead mount A is completely driven out and at the same time, with vacuum cock 7 opened, evacuation is continued until the degree of vacuum within the bulb 4 attains l X 10' IO' mmHg. Then the contents of the electric furnace are removed and vacuum cock 2 is opened to evacuate gap 10 to a degree of l X 10 10"mmI-Ig.Thereupon, on the outside of external cover 11, high frequency heating ringshaped coil extending out of high frequency generator 14 is set at the level of high frequency heating ring 6 and electric current is passed through coil 15 to heat high frequency heating ring 6,

thereby fusing together, as shown in FIG. 5, bulb 4 and bead 5 of bead mount a.

After fusion, the current supply to high frequency heating coil 15 is cut off; and after several minutes, the fused portion becomes smooth as a result of the residual heat. Thereafter, with both vacuum cocks 7, l2 shut and both air release cocks 8, 13 opened in both evacuating circuits C C air is introduced into the inside and outside of bulb 4. Thereupon with high frequency heating coil 15 disassembled from the external cover ll, external cover 11 and bulb 4 disassembled from evacuation equipment C, and holding cap b disassembled from bulb 4, the unnecessary bottom fused portion of the bulb 4'is cut off, as indicated in FIG. 5, by a cutter 38, to produce a small electric bulb d. 1

In the evacuation equipment C used here, a bulb inse'rtion opening 16 with a diameter larger than that of the bulb 4 is centrally bored and the end of evacuating circuit C,, equipped with a vacuum cock 7 and an air release cock 8, is connected to a charge-discharge hole 9, with a diameter smaller than that of bulb 4, which communicates with bulb insertion opening 16; an external cover-fitting slot 17 to receive the bottom of external cover 11 is provided around bulb insertion opening 16, and a charge-discharge hole 18 communicating with bulb insertion opening 16 is bored on the side surface, of the equipment, thereby connecting chargedischarge hole 18 to evacuating circuit C equipped with vacuum cock 12 and air release cock 13. Holding cap b for high frequency heating ring 6 is made as indicated in FIG. 3 by providing an adequate number of slits 19 in a longitudinal direction on the underside of a thin metal plate cylinder to impart elasticity to the underside of said cylinder, providing pointed legs 20 on the top side of said cylinder, fixing a high frequency heating ring 6 to the tips of said legs, partially bending a longitudinal portion of said cylinder outwardly and then inwardly to extend from the side of ring 6 to its top side, and forming at the tip of the extension an approximately semi-circular bulb-clamp 21 to hold the top side of bulb'4. The above description of the equipment and the process of manufacturing small electric bulbs according to the invention is, however, not restrictive.

In the Figures, 22 is an airtight rubber packing which is provided to serve concurrently to fix the bulb to the bottom edge in insertion opening 16; 23 is an airtight rubber ring which fits into the external cover-fitting slot 17; and 38 is a cutter with which the unnecessary portion of bulb 4 is to be cut off after completion of fusion between bulb 4 and head 5 of bead mount a.

Referring now to FIGS. 2, 4, S and 6, the difference of this embodiment from that of FIG. 1, etc., lies in the heating element for fusing together bulb 4 and bead 5 of bead mount a. The heating element is not a high for type but a resistance type; also an electric conductor FOR passing the current to the resistance heating element is attached to evacuation equipment C. The holding cap b, in this embodiment is made, as shown in FIG. 4, by providing an adequate number of slits 19 in a longitudinal direction on the underside of a thin metal plate cylinder to impart elasticity to the underside of said cylinder, forming pointed legs 20 on the top side, fixing an insulation ring 24 to the points of'said legs 20, providing a pair of semi-circular conductive plates 25, 26, not in contact with each other, around said insulation ring 24, brazing both ends of a resistance heating element 29 of say, nichrome wire, bent in ring form across a pair of heating element fitting pieces 27, 28 embedded adjacent to conductive piates 25, 26 on the insulation ring 24, bending a longitudinal portion of said cylinder outwardly and then inwardly to extend from the side of insulation ring 24 to its top side, and at the tip of the extension forming an approximately semicircular bulb-clamp 21 to hold the top of the bulb 4.

Meanwhile, the conducting pieces to pass the current to the resistance heating element 29 constitute a pair of conducting pieces 30, 31 made of phosphor bronze spring plates oppositely positioned between .bulb insertion opening 16 and the external cover insertion slot 17 along a straight line passing through the center of bulb insertion opening 16, said pieces 30, 31 being connected through conductive rods 34, 35 respectively to the terminals 32, 33 outside of the evacuation equipment C. Terminals 32, 33 are connected via cords 36,

37 to the power source. In other respects the arrangement is the same as that of FIG. 1. v

To manufacture small electric lamps using the equipment in this embodiment, described in connection with FIG. 1, bend mount a is inserted in bulb 4; holding cap b is fitted on the outside of bulb 4 and the bottom of bulb 4 is rigidly held in the bulb insertion opening 16 of evacuation equipment C. Thereby bulb 4 is inserted and fixed in bulb insertion opening 16 in such a manner that conductive plates 25, 26 around insulation ring 24 may respectively touch different conducting pieces 30, 31. Then over the entire assembly an external cover 11 is provided and the bottom of said cover is fitted rigidly into external cover fitting slot 17. Thereafter, in the same way as in connection with FIG. 1, bulb 4 is evacuated to 1 X l0' IO' mmI-Ig. and gap is evacuated to l X 10- 10"mmI-Ig. Then. with the power source closed, current is supplied to resistance heating element 29 for heating, thereby fusing together bulb4 and bead 5 of bead mount a. I I

After fusion is completed, the power supply to resistance heating element 29 is cut off; then in the same way'as previously described, the fused portion is made smooth; fused bulb 4 is taken out of the evacuation equipment; and with the unnecessary portion cut off as indicated in FIG. 5, the final product, small electric lamp d, is obtained.

In the foregoing embodiments, the degree of vacuum within the bulb or within the space between bulb and external cover, the temperature of the heating element and the duration of heating depend on the bulb size, the wall thickness, and the bead size of the bead mount in the small electric lamp to be manufactured.

Although there is no exact numerical limitation on the degree of vacuum outside of and inside of the bulb, the degree of vacuum should be greater on the inside than on the outside so that the difference in pressure and surface tension promotes contact between the bead and bulb during fusion. The exact conditions can be easily predetermined using known technical means.

For purposes of comparison, the manufacture of small electric lamps in accordance with conventional methods is to be described hereinafter with reference to the corresponding drawings.

Method 1 (FIG. 7)

FIG. 7 illustrates the state immediately before evacuation. In the Figure, an airtight box 41 is equipped with an exhaust pipe 42 leading to the exhausting equipment and an air release pipe 43 to communicate with the atmosphere. These pipes are each provided with a vacuum cock 44 and an air release cock 45. Lid 46 is dismountably fitted to airtight box 41; this lid is constructed rugged enough to withstand the conditions when airtight box 41 is sealed and evacuated. Mount-support rod 47 is slidably inserted at the center of [M46 without breaking the airtight condition of lid 46. This rod has a mount grip 48 at its bottom and it is elastically held to the lid by means of astopper 49 fixed at its top and a spring 50 movably fitted beneath this stopper. A heating element 51 is installed within airtight box 41. This element consists of a nichrome wire or the like formed in a coil; it is located surrounding fringe 52' of bulb 52 installed in a predetermined position in airtight box 41 and it is connected to an external power source. Element 53 is a ring-shaped support, and 54 is a support stand. Both are placed within airtight box 41 to support bulb 52 therein at a predetermined position. Bead mount a comprises a pair of lead wires 56, 57 fitted to its bend 55 and a filament 58 attached to the tips of these wires. The bead mount is inserted into bulb 52, with the ends of the lead wires held by mount grip 48, in such manner that bead 55 may be positioned nearly at the same level as fringe 52' of the bulb.

Next, to describe the manufacture of small electric lamps using this equipment, at first vacuum cock 44 is opened to fully exhaust the air out of airtight box 44; then cock 44 is shut. Thereafter, current is passed to heating element 51; heating element 51, when hot, heats bulb fringe 52 to a temperature high enough to soften and melt. Thereby fringe 52' contracts inwardly to narrow the mouth of bulb 52 until it approaches to lead wires 56, 57. At the same time, bead 55 also softens and melts to seal up the lead wires, whereupon the current supply to heating element 51 is cut off, and mount support rod 47 is depressed to join bead 55 and bulb fringe 52', thereby fusing themtogether to seal up bulb 52 airtight. Thus, the final product, a small electric lamp, is obtained. Method 2 (FIGS. 8, 9) e To manufacture a small electric lamp by this method, at first a bead mount a with a bead 60 wide enough to be able to engage the open edge of bulb 59 is inserted, with the filament down, into inverted bulb 59. Then this bulb is inserted, with bead 60 and the fringe of bulb 59 exposed, into a hole bored on the top of a jig 61 fabricated of a material, such as carbon or metal, which does not fuse to glass and is heat-resistant. In this state jig 61 is placed in a heating furnace. The heating furnace contains a tube 62 made of heat-resistant material like quartz or metal; heating resistant wire 64 is wound around the outside of heating part 63 near the midpoint of tube 62, and heating part 63 is wrapped with a heatshielding material 65, such as magnesia, and further outside a surrounding wall 66 is provided. Lead terminals 67, 68 of heating resistance wire 64 are provided on the surrounding wall. Respectively at inlet 69 and outlet 70 to tube 62 are installed air-insulating doors 71, 72; and midway between these doors 71, 72 and heating part 63 are positioned exhaust pipe 73 to evacuate tube 62 and air release pipe 74 to introduce air into tube 62. Inside of tube 62 a support stand 75 is arranged to carry jig 61; and to this stand 75 is fitted a metal wire 76 by which stand 75 is carried from inlet 69 to outlet 70.

Jig 61 is carried on stand 75. By manipulation of metal wire 76, jig 61 is positioned at heating part 63 within the tube 62,; and air is exhausted to create a vacuum by closing inlet 69 and outlet 70 and opening cock 73 of exhaust pipe 73 in tube 62.

Then, current is passed to make the heating element hot, whereupon radiant heat from the inside wall of tube 62 melts and softens the exposed bead 60 and the fringe of bulb 59 on the top of jig 61, thereby effecting the seal. After fusion and sealing, cock 73 of exhaust pipe 73 is closed and cock 74' of air release pipe 74 is opened to introduce air into tube 62; and by manipulation of metal wire 76 with the doors 71, 72 being open, jig 61 is carried out of tube 62, providing the finished product, a small electric lamp.

Method 3 (FIG. 10)

To manufacture a small electric lamp by this method, at first the entire bead mount a, with lead wires 1, 2 outstretched, is inserted into bulb 4 and, utilizing the elasticity of lead wires 1, 2, bead mount a is fixed in position within bulb 4. i

Next, the open end of bulb 4 is airtightly connected to exhaust pipe 77 communicating with the exhausting equipment; bulb 4 is exhausted to vacuum; thereafter from both sides of bead mount a at the outside of bulb 4, gas burners 78, 79 are applied to melt and soften the part of bulb 4 to be fused and bead 5 of the bead mount a,' thereby fusing them together. After fusion, exhaustion by exhaust pipe 77 and heating by gas burners 78, 79 are halted; bulb 4 is disconnected from exhaust pipe 77; and the unnecessary portion of the bulb is cut off to produce finally a small electric lamp.

As fully described above, these conventional methods (l3) for manufacturing small electric lamps have many drawbacks. All of these drawbacks are completely eliminated from the method of manufacturing small electric lamps, the electric lamps thus produced, and the manufacturing equipment, according to the present invention. Namely, the present invention offers a manufacturing method based on a double evacuation method of evacuating both the inside and outside of the bulb; when the equipment and the method illustrated in the embodiments of this invention are used to fuse together the bead of the bead mount and the bulb, not only the impure gas generated from the heating element and other parts is not allowed to infiltrate into the bulb, but also perfect fusion can be assured by appropriately selecting the pressure difference between inside and outside of the bulb in accordance with predetermined manufacturing conditions, such as the bulb wall thickness, etc. Thus there is no likelihood of deformed fusion of the bulb, insufficient fusion or fusion strain. As in the embodiment of FIG. 1, when a high frequency heater is adopted as the power source for fusion of the bead of the bead mount to the bulb, the heat from the high frequency heating ring and the self-induction heat from the bulb and the bead-glass in a semi-molten state develops a self-induction heat, which promotes heating and melting of the part to be fused and produces a more perfect, reliable and smooth fusion.

Small electric lamps produced by the method and equipment of the present invention have perfectly 5 fused bulbs which contain no impure gas; therefore they are not likely to develop cracks or slow leaks under varied temperature and vibration in service.

Thus, the method of the invention can simplify mass production of high quality small electric lamps with no deterioration of illumination and with maximum service life. Moreover, since the equipment is simplified and its operation is easy, the manufacture requires no skilled labor. Thus, even a non-skilled worker can produce the lamps without any loss because of rejects. Besides, the equipment can be readily automated for mass production with increased efficiency. Meanwhile, annealing, to correct the deformation of the joint after I the fusion of bead and bulb is completed, is obviated and in consequence the finished product can be low in cost.

As seen from the above description, the method of manufacturing small electric lamps according to this invention, small electric lamps thus produced, and the manufacturing equipment to be used, have a number of industrial advantages over the conventional methods of manufacturing small electric lamps, small electric lamps thus produced and the manufacturing equipment to be used therewith. 1

What is claimed is:

l. A method of manufacturing small electric lamps comprising a. inserting a filament-attached bead mount at a predetermined position within a bulb;

b. placing the bulb in an evacuation zone in a manner such that the interior and exterior of the bulb are in communication with separate evacuation means;

c. separately evacuating the interior of said bulb and said zone surrounding said bulb;

d. heating the bulb in thearea adjacent the bead mount to cause melting of the bulb wall and fusion of the bulb to the bead of the bead mount;

e. gradually cooling the fused portion of the bulb to create a smooth seal at the point of fusion;

f. removing the fused bulb from the evacuation zone;

and

g. cutting of the unnecessary portion of the bulb below the point of fusion to provide a small electric lamp.

2. The method of claim 1 wherein the degree of vacuum within the bulb is l X 10" to ltfimml-lg. and the degree of vacuum in the evacuation zone is l X 10 to IO-mmI-Ig.

3. The method of claim 1 wherein the bulb is heated 5 by a high frequency carbon heating element.

4. The method of claim 1 wherein the bulb is heated by a resistance heating element. 

1. A method of manufacturing small electric lamps comprising a. inserting a filament-attached bead mount at a predetermined position within a bulb; b. placing the bulb in an evacuation zone in a manner such that the interior and exterior of the bulb are in communication with separate evacuation means; c. separately evacuating the interior of said bulb and said zone surrounding said bulb; d. heating the bulb in the area adjacent the bead mount to cause melting of the bulb wall and fusion of the bulb to the bead of the bead mount; e. gradually cooling the fused portion of the bulb to create a smooth seal at the point of fusion; f. removing the fused bulb from the evacuation zone; and g. cutting of the unnecessary portion of the bulb below the point of fusion to provide a small electric lamp.
 2. The method of claim 1 wherein the degree of vacuum within the bulb is 1 X 10 6 to 10 8mmHg. and the degree of vacuum in the evacuation zone is 1 X 10 2 to 10 4mmHg.
 3. The method of claim 1 wherein the bulb is heated by a high frequency carbon heating element.
 4. The method of claim 1 wherein the bulb is heated by a resistance heating element. 